An intake valve or an exhaust valve of an internal combustion engine may bite a deposit between a valve and a valve seat that are formed in a valve head. The biting of the deposit might cause compression leakage in a cylinder and accidental fire. Chewing of a deposit by rotating a valve is suggested as a countermeasure of removing a deposit that is bitten between the valve and the valve seat. A valve rotator that can be applied to the suggestion is being known (for example, with reference to Patent Document 1).